This invention relates to a process for separating polysaccharides from tamarind seeds. More particularly, this invention relates to a process for producing commercially from tamarind seeds a high grade of powdered polysaccharides at low cost and by simple operations.
Tamarind seeds are seeds of a tall tree, Tamarindus indica, which grows in the tropics. In general, the tamarind seeds contain only 45-55% by weight of polysaccharides, which are intricately mixed with other ingredients such as proteins and fats, so that the polysaccharides in the tamarind seeds are notably difficult to separate. The polysaccharides are generally contained in a seed portion called the albumen, which can be separated without difficulty from the rest of the seed. However, tamarind seeds differ from other seeds, such as locust bean seeds and guar seeds, in that the albumen also contains proteins even after it is divided into fine particles. Thus the separation of the polysaccharides from the tamarind seeds is more difficult than in other seeds, and requires special means.
On the other hand, the polysaccharides obtained from tamarind seeds have good properties which polysaccharides from other sources do not have. For example, the polysaccharides from tamarind seeds are stable against acids, and are widely used as a thickening agent or a gelling agent in the food, paper and fiber industries. If polysaccharides which are used in these fields contain proteins and fats as impurities, these polysaccharides would form an aqueous solution which is liable to generate foams, to lose fluidity, or to form deposits. Thus polysaccharides from tamarind seeds are considered to be of low quality for this reason. Accordingly, in order to obtain polysaccharides of a high quality from tamarind seeds, it is necessary to purify the thus obtained polysaccharides to remove proteins and fats therefrom as much as possible.
Various attempts have been made to remove proteins and fats from polysaccharides obtained from tamarind seeds. All these attempts include the steps of first pulverizing the tamarind seeds to form powders, and then treating the powders with air, water, or an organic solvent. All these methods, however, require many complicated steps as described below, and hence are unsatisfactory.
Japanese Unexamined Patent Publication No. 52-111597, which corresponds to U.S. Pat. No. 4,074,043, discloses a method wherein the tamarind seeds are first pulverized to form powders of a particle size of less than 100 microns, then the powders are separated by air classification into a fraction rich in proteins and a fraction rich in polysaccharides. However, in order to carry out this separation effectively, it is necessary to remove fats beforehand by treating the powders with an organic solvent, which makes the process intricate and troublesome. If the fats are not removed, the powders become tacky and are difficult to disperse in air.
Japanese Examined Patent Publication No. 40-18120 discloses a method wherein the tamarind seeds are first subjected to extraction by hot water, and the resulting extract is coagulated by an inorganic sulfate. However, this process has disadvantages in that it is complicated, the cost of the extraction by use of hot water is high, the yield is poor, particularly in view of the high cost, and it is difficult to remove completely the salts which have been added for the coagulation step.
Japanese Examined Patent Publication No. 42-14034 discloses a method wherein tamarind seed powders are dispersed in an organic solvent to form a dispersion, and the polysaccharide powders are recovered from an underlayer of this dispersion using the difference in density between the solvent and the powders. However, this process requires that the powders are washed beforehand with water, then filtered and dried. As a result, the process has the disadvantage of being complicated.
Japanese Unexamined Patent Publication No. 60-118152 discloses a method wherein the proteins in the tamarind seed powders are decomposed and solubilized by a proteic enzyme. However, if the tamarind seed powders are treated in accordance with the process taught in this publication, then fats cannot be removed from the polysaccharides. As a result, the polysaccharides tend to become swollen in hot water, which renders the subsequent steps of filtration and washing difficult
As mentioned above, all the attempts hitherto made to obtain polysaccharides of a high grade from tamarind seeds were not satisfactory, required intricate steps, and therefore could not be advantageously carried out on a commercial scale.